A 30-year-old man charged with murder after the fatal shooting of two Dallas hospital employees was on parole and had been given permission to be at the facility for the birth of a child, a Texas prison official has said.

Nestor Hernandez was granted leave to be with his “significant other” at Methodist Dallas Medical Centre during her delivery on Saturday, according to a Texas Department of Criminal Justice spokeswoman.

She said he had been sentenced to prison for aggravated robbery and was released on parole last October, but did not provide additional details on the circumstances of the shooting.

Authorities have said Hernandez opened fire at the hospital around 11am on Saturday and killed two staff members before being shot and injured by a hospital police officer. It is unclear what led to the shooting.

Hernandez, who was wearing an ankle location monitor at the time, was taken to another hospital for treatment, hospital officials said.

The Texas prison system’s Office of Inspector General is working with police to investigate the shooting, the spokeswoman said. Dallas police and a hospital spokesman declined on Sunday to provide additional information on the shooting.

It follows hospital shootings in September in Little Rock, Arkansas, that killed a visitor and one in June in Tulsa, Oklahoma, that left four dead.